Ultrasonic surgical instruments are known which include ultrasonic surgical shears having an ultrasonic surgical blade, a clamping arm operable to open and close toward the blade, a tissue pad attached to the clamping arm and including a 0.033 square-inch clamping surface area, and a device for exerting a 1.5 pound clamping force on the clamping arm which creates a clamping pressure of 45 psi (pounds per square inch) on a blood vessel which is positioned between the clamping surface area of the tissue pad and the blade. It is noted that the clamping surface area is the area where the blade and the tissue pad are in close proximity when the clamping arm is in a closed position. Exemplary devices are described in U.S. Pat. Nos. 5,322,055 and 6,325,811, the contents of which are incorporated herein by reference. The result of the ultrasonically-vibrating ultrasonic surgical blade and the clamping pressure on the blood vessel is a coaptation of the blood vessel (a bringing together of the walls of the blood vessel), a transection (a cutting) of the coaptated blood vessel, and a coagulation (a sealing) of the coaptated cut ends of the blood vessel. It is known that blood-vessel transection times can be decreased with the application of a higher clamping force. However, this is not done because conventional thought is that decreasing the blood-vessel transection time using a higher clamping force will lead to a degradation in coagulation performance (i.e., a lowering of the burst pressure of a sealed end of the transected blood vessel). Conventional ultrasonic surgical shears are not used on blood vessels larger than 3 mm because the clamping force used is inadequate for proper coaptation.
Still, there is a need in the medical device industry for improved ultrasonic surgical shears and improved methods for sealing a blood vessel using an ultrasonic surgical shears.